Moina affinis. 
291 
little proximad to the middle and its length is about one-half 
that of the antennule. The antennules are fringed on the pos¬ 
terior side by a dense growth of very fine hairs, visible only 
with a high power of the microscope, but easily disclosed by 
treatment with osmic acid. 
The antennae resemble in general those of M. propinqua. 
Transparent, with sometimes a tinge of violet. 
Length, 0.8-1 mm. Height, 0.4-0.5 mm. 
Male—The male is about 0.3-0.6 mm. in length, and agrees 
in structure with the usual type of the males of this genus. 
The antennules are modified into powerful claspers. They are 
broad at the base in the antero-posterior direction and are in¬ 
serted near the vertex, so that the head projects but little be¬ 
yond them. They are geniculate, the angle occurring about 
1-5 of the length from their insertion. At the bend are two 
sense hairs, one short and stout and the other long and slender. 
There are four hooks at the distal end of the antennule. 
The first foot has a hook and is without a flagellum. 
The spermatozoa are spherical or oval, and never have radiate 
projections of protoplasm. 
This species is evidently close to the European M. rectirostris , 
Jur. I have been somewhat in doubt as to the specific distinct¬ 
ness of the form, but on the whole I have thought it best to 
give it a separate name, although recognizing the possibility 
That the range of variation of M. rectirostris will be found great 
enough to cover this form. It is clear that If. rectirostris , Jur., 
of Europe, M. propinqua , Sars, of Australia, and M. affinis are very 
closely allied species. They agree in general form, color and 
size. All have an ephippium with one egg, and a head with 
supra-ocular depression. All agree in number and structure 
<of the anal teeth and in the size of the bident. The legs prob¬ 
ably agree in structure. Those of iff. rectirostris and M. affinis are 
alike, but Sars says nothing specific of the structure of those 
of M. propinqua and does not differentiate the European species 
M. rectirostris and M. brachiata . 
The males of the three species agree in general form. They 
.have the bend of the antennule proximad to the middle of its 
